Difference between sphere and cube specific surface area calculation
Factors affecting the surface area include particle size (particle size) and particle shape (grain shape) as well as pore content. Imagine a real cube that is one meter long and is cut into small cubes of one micron (10 -6 μm). This will produce 1018 particles.
The area exposed by each particle is 6x10-12 square meters (m2), and the total area contributed by all particles is 6x106?m2. A million-fold increase in this exposed area compared to uncut materials is typical of ultra-fine powders having a large surface area. In addition to the particle size, the particle shape also contributes to the surface area of ​​the powder. In all geometries, the sphere has the smallest area/volume ratio, but a string of atoms will have the largest area/volume ratio if only bonded along the chain axis. All particulate matter has a geometric shape and thus has a surface area between the two extremes. The effect of particle shape on surface area is readily seen by comparing two surface areas of particles having the same composition and the same mass, but spherical and cubic, respectively. It is calculated that the cube area is larger than the sphere area with the same particle weight. Because of the difference in particle size, grain shape, and porosity, the range of specific surface area can vary greatly, but the effect of pores tends to completely obliterate the effects of particle size and external shape factors. A powder consisting of 0.1 micron radius spherical particles with a density of about 3 g/cm3? has a specific surface area of ​​about 10 m2/g, while a similar particle with a 1.0 micron radius is 10 times smaller than the surface; but if the same 1.0 micron radius particles contain a large amount The pores may have a specific surface area exceeding 1000 m2/g. This clearly indicates the important contribution of the pore to the surface area. ?
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